Source: http://www.abarim-publications.com/Meaning/Ahumai.html

🔼The name Ahumai in the Bible

The only Ahumai in the Bible is a son of Jahath, who is a son of Reaiah, who is a son of Shobal, who is a son of Judah, one of the sons of Jacob and name-giver to one of the tribes of Israel (1 Chronicles 4:2). Apart from this note in Judah's genealogy, we hear nothing further about this person.

🔼Etymology and meaning of the name Ahumai

The origin and meaning of the name Ahumai is a bit of a mystery. Alfred Jones (Dictionary of Old Testament Proper Names) takes it from (1) the word אח (ah), meaning brother, or figuratively, friend or close associate, and (2) a forced singular form of the common plural word מים (mayim) meaning waters:

NOBSE Study Bible Name List apparently draws towards the verb חמם (hamam), meaning to be hot or warm, and the adjective חם (ham) meaning hot (see the name Ham). The final yod could be a remnant of יה (Yah) = יהו (Yahu) = יו (Yu), which in turn are abbreviated forms of the Tetragrammaton; the name of the Lord: YHWH. Hence NOBSE translates this name with Heated By Yahweh, which would be a perfectly acceptable Biblical sentiment but requires stretching the evidence pretty thin.

And while we're stretching: the name Ahumai could also be regarded as a construct of (1) the word אחו, a collective noun meaning reeds or rushes, as used in Genesis 41:2 and Job 8:11; and (2) the interrogative particle מי (mi), meaning who? That would render the whole name Ahumai the meaning of Who's The Reeds?, which, we admit, is rather silly. But perhaps Jones is on to something and the final part has to do with מים. The trouble is that the assumed singular form מי may have not at all existed. The plural word מים occurs almost 600 times and may in essence be compared to our word "people," which is a plural word too (people are) but not constructed from an assumed singular word peop.

Still, the word Ahumai may have reminded some among a Hebrew audience of a meaning like Sea Of Reeds.

BDB Theological Dictionary stays out of the discussion on the meaning of our name all together and does not translate nor hints at possibilities.